1. Field of the Invention
The present invention relates to an image synthesizing system using a depth cueing technique and a video game apparatus using such an image synthesizing system.
2. Related Art
There is known an image synthesizing system which uses the computer graphics technique to synthesize a pseudo 3-D image. Such an image synthesizing system is broadly used in various applications such as video games, various simulators and others.
Such an image synthesizing system uses a depth cueing technique in which the brightness in a polygon is varied depending on the distance between that polygon and the view point.
The image synthesizing system of the prior art has such a problem that the depth cueing is not carried out while reducing the burden on the hardware.
In the image synthesis through the depth cueing technique, the brightness of a polygon is varied depending on its Z coordinate representing the distance between that polygon and the view point in a virtual 3-D space so that the polygon will fade into the background in the direction of depth.
However, the prior art requires to provide memories equal in number to N for color palettes into which color information is to be written if the brightness of the polygon in the direction of depth is to be progressively varied through N steps (where N is an integer) depending on its Z coordinate. For example, the base color may be written into the first palette; the next color may be written into the second palette; . . . and a color faded into the background may be written into the final or N-th palette. When the brightness of the polygon is to be smoothly varied through such a technique, a great number of palettes must be provided. This correspondingly increases the memory capacity, leading to increase of the manufacturing cost of the entire system.
Particularly, in the present image synthesizing systems, a great number of basic palettes are frequently used to represent colors delicately. In such a case, if the number of basic palettes is equal to M, palettes equal to MxN in number must be provided. This further increases the memory capacity.
The burden on CPU used for calculation increases correspondingly. Thus, it could not be avoided that the entire system would be more expensive and complicated.
In view of such problems of the prior art, an object of the present invention is to provide an image synthesizing system of simpler structure capable of performing the depth cueing and a video game apparatus using such an image synthesizing system.